Microbial hydrocolloids are widely used in food industry, among which food-grade gellan gum is an important product. Gellan gum is usually in two forms: high acyl (HA) gellan gum and low acyl (LA) gellan gum. Low acyl gellan gum can be obtained by deacylation during the extraction of gellan gum fermentation broth. According to the transparency, low acyl gellan gum can be divided into two types: transparent type, and non-transparent type. The degree of transparency is related to the content of impurities contained in gellan gum. High transparent low acyl gellan gum can be obtained if the impurities are completely removed.
To the best of our knowledge, in known preparation techniques of low acyl gellan gum, fermentation broth must be pretreated and separated, and then water is added at high temperature to dissolve for deacylation. The disadvantages of current techniques are complicated operation, numerous steps, low product quality caused by easily hydrolysis of gellan gum during production, and high consumption of water and energy. In addition, one-step filtration is disclosed in the preparation of transparent low acyl gellan gum (such as CN101665778A), however, such filtration is not thorough enough and results in high content of impurities and low transmittance. Two-stage filtrations are also disclosed (such as CN1766120A, CN1351172A), where membrane is applied as filter media in second filtration. The disadvantage is that only small molecule gellan gum can pass through the small-size pores of membrane, while large molecule gellan gum is retained, resulting in low yield and less application value. To the best of our knowledge, there has been no report for preparing low acyl gellan gum by two-stage filtrations, wherein diatomite and/or perlite with different particle sizes is applied as filter media and filter aid.
The present invention provides a method for preparing high transparent low acyl gellan gum, including directly deacylation on fermentation broth, and carrying out two-stage filtrations, wherein diatomite and/or perlite with different permeabilities is used as filter media and filter aid.